Over the years, there has been a steady progression in the development of techniques that are useful for fluidizing material in a vibrating bed for a wide variety of different applications. The material to be fluidized is typically granular in nature such as, for example, sand, and a gas such as air is used to fluidize the material. More particularly, the gas is pressurized and then directed into a plenum chamber which permits the pressurized gas to pass through a vibrating material-supporting bed.
Typically, the vibrating bed will comprise a perforated plate or porous membrane which is known as a distributing deck. As will be appreciated, the distributing deck serves the purpose of permitting the pressurized gas to pass into the material.
Of course, the supporting bed must be in communication with the plenum chamber and must have openings in order for the pressurized gas to pass into the material which is to be fluidized. It is commonly the case that the gas is at a sufficient velocity and pressure that the material, even though granular in nature, cannot pass through the relatively small openings in the bed into the plenum chamber. However, if there is a failure in the equipment that pressurizes the gas, the granular material can pass through the openings in the bed requiring its removal from the plenum chamber.
In other words, a vibrating fluidized bed assembly is typically operated by producing pressurized gas in advance of the actual introduction of the granular material. Then, when the granular material is supplied to the bed above the plenum chamber through the air distributing plate or deck, the velocity and pressure of the gas is sufficient to prevent the granular material from passing through the openings in the bed under normal operating conditions. Subsequently, the granular material is removed from the fluidized bed in advance of discontinuing the supply of pressurized gas to the plenum chamber.
As a result, the granular material will usually not pass through the openings in the bed into the plenum chamber unless there is a loss of pressure that occurs for some unexpected reason such as a power failure or equipment failure. This will typically not occur, but the difficult and time-consuming task of removing the granular material from the plenum chamber, if it should occur, is a matter for serious concern due to the potentially adverse consequences. For instance, if the granular material was being fluidized at the moment of an equipment failure and the vibrating motion would continue, the granular material would pass through the openings in the distributor deck causing material leakage to the plenum chamber.
Not uncommonly, the clean-up task requires the disassembly of the equipment to a significant degree in order to reach the interior of the plenum chamber. In a vibrating fluidized bed assembly where the plenum chamber is integral with the distributor deck, continued vibratory motion will cause material to sift and accumulate in the plenum chamber. This makes it impossible to use the equipment for the intended purpose for an undesirably long period of time and requires a significant amount of manual labor. Clearly, there is a need to be able to ensure that the material will not pass into the plenum chamber under any circumstances even in the event of a power failure or equipment failure. However, there is also a recognition that any proposal for accomplishing this objective must not interfere with the effectiveness of the fluidization process. This has attempted to be achieved in the past by utilizing a mushroom-shaped cover over each of the openings in the bed to prevent the material from passing therethrough. Unfortunately, this has not been fully satisfactory due to the complexity and cost and because articles that are placed in the fluidized material can become caught on these covers.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects.